1. Field of the Invention
The invention is directed to valves for controlling fluids in systems such as fuel injection systems for internal, combustion engines.
2. Description of the Prior Art
One such valve is described in European Patent Disclosure EP 0 477 400 A1, for instance, in which the deflection of a piezoelectric actuator is transmitted via a hydraulic chamber that functions as a hydraulic booster or tolerance compensation element and encloses a common compensation volume between two pistons defining this chamber, one of which is embodied with a smaller diameter and connected to a triggering valve closing member, and the other of which is embodied with a larger diameter and is connected to the piezoelectric actuator. Thus the actuating piston executes a stroke that is lengthened by the boosting ratio of the piston diameter, when the larger piston is moved a certain distance by the piezoelectric actuator.
This known valve is intended to separate a low-pressure region from a high-pressure region and can for instance be used in fuel injectors, in particular common rail injectors, or pumps of motor vehicles, where such valves are also known in various versions in the industry.
If such a valve is to be functional, the hydraulic system requires a system pressure in the low-pressure region, especially in the hydraulic coupler, but this system pressure drops as a function of leakage unless adequate replenishment with hydraulic fluid takes place. As a rule, a filling device is therefore provided, with which pressure medium from the high-pressure region can be resupplied to the system pressure region.
For common rail injectors, solutions to this problem are known in the industry, in which the system pressure, which is expediently generated in the valve itself and should also be as constant as possible upon system starting, is assured by delivering hydraulic fluid from the high-pressure region of the fuel to be controlled to the low-pressure region, where system pressure prevails, with the aid of leakage gaps, represented for example by leakage or filling pins. Typically, the system pressure is adjusted by a valve and can for instance also be kept constant by plurality of common rail valves.
A system pressure in the hydraulic chamber that is essentially constant and is at least largely independent of the prevailing high pressure in the high-pressure region presents the problem, however, that at high pressure values, great actuator force is required to open the valve closing member counter to the high-pressure direction, which this dictates a correspondingly large, cost-intensive dimensioning of the actuator unit. Furthermore, at high pressure in the high-pressure region, the positive displacement of hydraulic volume out of the hydraulic chamber via the gaps surrounding the adjacent pistons is reinforced accordingly, meaning that under some circumstances, the refilling time for building up and maintaining the counterpressure on the low-pressure region is prolonged, so that for lack of complete refilling, in the event of a re-actuation of the valve soon thereafter, a shorter valve stroke will be executed, which can adversely affect the opening behavior of the entire valve.
The valve of the invention for controlling fluids has the advantage that the system pressure is variable in a structurally simple way as a function of the pressure prevailing in the high-pressure region. Because of the high-pressure-dependent refilling, at a high pressure level in the high-pressure region an increase in the system pressure in the hydraulic chamber is possible, as a result of which the actuating piston is reinforced for opening the valve closing member counter to the existing high pressure. Advantageously, a reduced trigger voltage of the actuator unit is thus required, compared to a valve with a constant system pressure, and the valve of the invention can therefore be equipped with a smaller, less expensive actuator unit. The valve of the invention also makes a defined filling of the low-pressure region, especially the hydraulic chamber, possible. When the pressure in the high-pressure region is increasing, with the variable system pressure the refilling time can be shortened.
Structurally, the embodiment according to the invention is distinguished by its simplicity, which makes it possible to define the variable system pressure in the hydraulic chamber by means of easily adjustable geometric variables such as the diameters and lengths of the throttle body and of the piston, along which the system pressure is reduced toward the low-pressure region. Along with the low costs for production and assembly, above all the resistance of the system pressure supply to particles or dirt in the hydraulic fluid is advantageous; this can be ascribed to designing the refilling device with a quasi-secondary flow. The secure furnishing of the requisite system pressure over the entire engine performance graph is thereby assured.
In an especially advantageous version, it can be provided that the at least one throttle body is axially adjustably disposed in the hollow chamber and is preferably movable such that it at least partly intersects the branching point of the system pressure line when the system pressure drops. Thus the length of the gap around the throttle body through which a flow is required is shortened, resulting in a higher flow rate and an increase in the system pressure.
The valve according to the invention is especially well suited to triggering fuel injection valves, but in principle it can also be realized in all hydraulically boosted systems with a piezoelectric actuator or with a magnetic final control element, such as in pumps.
Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims.